To facilitate the reader's understanding of the present invention, the CPB process is generally described below, followed by a description of the problems with vascular clamps used during the CPB process in the past.
The descriptive terms upstream and downstream, when used herein in relation to the patient's vasculature, refer to directions closer to and further from the heart in the arterial system, and the opposite in the venous system. The terms proximal and distal, when used herein in relation to instruments, refer to directions closer to and farther away from the operator of the instrument, respectively.
During CPB, it is desirable to provide life-support functions, a motionless, decompressed heart and a dry, bloodless field of view for the surgeon. In a basic CPB system, oxygen-poor blood is drained by means of gravity or is syphoned from the patient's venous circulation and is transported to a pump-oxygenator, commonly known as the heart-lung machine, where the blood is exposed to a gaseous mixture that eliminates carbon dioxide and adds oxygen to the blood. The oxygenated blood is then returned or perfused into the patient's arterial circulation for distribution throughout the entire body. This process requires a venous drainage cannula (or cannulae) to be placed into the right side of the heart (typically the right atrium) or directly in the major veins (typically the superior vena cava (SVC) and/or inferior vena cava (IVC)) or through peripheral vein access sites to drain unoxygenated blood from the patient and deliver it to the heart-lung machine. Similarly, an arterial or aortic perfusion cannula is placed in the aorta or another large peripheral artery, such as the common femoral artery, to return or perfuse oxygenated blood to the patient. The heart and lungs of the person can thereby be effectively bypassed, thus allowing the surgeon to operate on a bloodless heart.
The insertion of the arterial (aortic) perfusion cannula is usually performed in the following fashion. After an incision is made in the patient's chest and the pericardium (the protective sac around the heart) has been entered, two concentric purse string sutures are placed into the anterior wall of the ascending aorta just proximal to upstream of the brachiocephalic trunk. A "choker" tube or sleeve is positioned over the trailing ends of the suture threads to act as a tourniquet for tightening the purse string suture. A small incision is then made through the wall of the aorta into its lumen in the center of the purse-string sutures. The aortic perfusion cannula is then quickly inserted through that incision into the lumen of the aorta, taking care to minimize the escape of blood from the puncture site. The purse string sutures are then tightened by means of their respective tourniquets to seal the aortic wall around the perfusion cannula in order to prevent the escape of blood from the aorta. Air is then evacuated from the perfusion cannula as it is joined by a connector to the tubing from the pump-oxygenator. A mechanical cross-clamp, i.e., vascular clamp, is placed on the ascending aorta just downstream of the aortic root and upstream of the cannula to ensure that no blood flows back into the aorta during CPB.
The venous drainage cannula(e) is (are) inserted in a similar manner directly through an incision in the right atrium of the heart or into the superior and/or inferior vena cava for connection to the drainage side of the pump-oxygenator. Once the requisite cannulae are in place and the connections are made to the heart-lung machine, CPB is instituted by allowing unoxygenated blood returning to the right side of the heart to be diverted through the venous drainage cannula(e) and into the pump-oxygenator where it is oxygenated and temperature-adjusted. From there, the blood is pumped into the patient's arterial system via the arterial or aortic perfusion cannula to provide oxygen rich blood to the patient's body and brain.
After CPB has been established, the process known as cardioplegia, which literally means "heart stop," is used to arrest the beating of the heart, and in some procedures, to provide oxygen to the myocardium. Cardioplegia is administered by delivering a cardioplegic solution, such as potassium, magnesium, procaine, or a hypoclacemic solution, to the myocardium by antegrade and/or retrograde perfusion. For example, cardioplegia may be administered by inserting a needle into the aorta upstream of the aortic cross-clamp and injecting cardioplegic solution into the aortic root. The cardioplegic solution drains in the normal direction of blood flow into the coronary ostia, through the coronary arteries, and into the capillaries within the myocardium.
The problems with conventional vascular clamps used during the CPB process will now be described. As previously mentioned, the vascular cross-clamp is placed externally on the ascending aorta through an incision or opening in the chest. Traditionally, when cardiac procedures are to be performed, the sternum is cut longitudinally (a median sternotomy), providing access between opposing halves of the anterior portion of the rib cage to the heart and other thoracic vessels and organs. Alternatively, a lateral thoracotomy is formed, wherein a large incision is made between two ribs. A portion of one or more ribs may be permanently removed to optimize access. Either of these techniques provides a substantial opening in the chest, giving the surgeon a relatively large working area through which to operate.
A problem with these techniques for accessing the heart area is that they cause the patient significant trauma. The patient requires immediate postoperative care in an intensive care unit, a total period of hospitalization of up to seven to ten days, and a recovery period that can be as long as six to eight weeks.
In more modern, minimally invasive cardiac surgery, smaller incisions are made in the chest at various strategic locations. The surgical instruments are introduced at these locations. An endoscope is provided at one of these locations, and selected surgical instruments are manipulated by the surgeon with the aid of the endoscope. Accessing the heart area with minimally invasive techniques causes the patient less trauma than the techniques described previously.
A problem with all of the aforementioned techniques for accessing the heart area, especially minimally invasive techniques, is that the access area or the incision area is very limited in size. The larger and/or the greater the number of surgical instruments, the more they interfere with the cardiac procedures to be performed.
Vascular clamps in the past have traditionally had long and/or large shafts and handles that tend to obstruct the access area during cardiac surgery. Some vascular clamps in the past have included "bulldog" clamps, or similar clamps, to alleviate this problem. A "bulldog" clamp is a small V-shaped clamp that is applied to a blood vessel with an applier, such as forceps, and left on the blood vessel until it needs to be removed. Once the "bulldog" clamp is applied to the blood vessel, the applier is removed from the operating site, reducing the interfering effect the cross-clamp has on the surgical procedure. A problem with "bulldog" clamps and related clamps is that they do not give the operator immediate control over the opening and closing of the clamp. If the clamp needs to be opened, an instrument, usually different than the applier, must be delivered to the surgeon, introduced through the incision, and used to remove the clamp. This opening process takes too long if blood flow through the clamped blood vessel is immediately necessary.
A need therefore exists for a vascular clamp that does not take up a significant amount of space at the operating site, yet provides the operator with immediate control over the clamp.
A problem with vascular clamps that relates more to minimally invasive cardiac procedures is that they typically have a construction that makes them difficult to introduce through a narrow insertion in the chest, and, once in the chest, they are difficult to manipulate around body tissue to the blood vessel to be clamped.
In the past, vascular clamps, once they were clamped to the blood vessel, are usually held in the closed position manually by the operator, or with a locking mechanism. Manually maintaining the clamp in the closed position is desirable in that it gives the operator a better feel for the pliability of the blood vessel; however, it also introduces the possibility of operator error. For example, too much pressure on the blood vessel will damage the blood vessel, and insufficient pressure will not preclude blood flow through the blood vessel. Particularly for clamps without attached handles, quick removal of the clamp is difficult if blood flow through the blood vessel becomes immediately necessary.
Therefore, a further need exists for a vascular clamp that includes a locking mechanism that allows for the immediate release of the clamp.